Chapter 15, Problem 15.141MP

Ethylenediamine (NH₂CH₂CH₂NH₂, abbreviated en) is an organic base that can accept two protons:

     $\begin{array}{l}\text{en}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)\rightleftharpoons {\text{enH}}^{\text{+}}\left(aq\right){\text{+ OH}}^{-}\left(aq\right)K_{\text{b}1}=5.2\times {10}^{-4}\\ {\text{enH}}^{+}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)\rightleftharpoons {\text{enH}}_2{}^{2+}\left(aq\right)\text{+}{\text{OH}}^{-}\left(aq\right)K_{\text{b}2}=3.7\times {10}^{-7}\end{array}$

(a)    Consider the titration of 30.0 mL of 0.100 M ethylenediamine with 0.100 M HCl. Calculate the pH after the addition of the following volumes of acid, and construct a qualitative plot of pH versus milliliters of HCl added:

(i)    0.0 mL

(ii)    15.0 mL

(iii)    30.0 mL

(iv)    45.0 mL

(v)    60.0 mL

(vi)    75.0 mL

(b)    Draw the structure of ethylenediamine, and explain why it can accept two protons.

(c)    What hybrid orbitals do the N atoms use for bonding?